I went into this as just a visual novel. Noticed that it was incest and that aspect of it kinda put me off even with the changed language of landlord and tenant. But I got stuck. Even when I got disturbed by some of the incestuous themes, it was hard to stop reading because the characters are so well written.
However to critique the current version. The blanket change from mum to landlady, dad to landlord and children to tenants makes it a little bit odd. Very few people would have any connection to their landlords and when the MC and Sandra talk about starting a family, it doesn't really make sense to keep talking about becoming landlords and tenants. I'm going to guess you have some changes in mind, since this is still in development, but I still think I can give an idea that I think could solve this issue to distance from incest. Make the MC be adopted by the MC's father, meaning no blood relations. Have Rebecca not be the mother at adoption but a step mother. This scenario would allow the relationships to not be incestuous but still retain all the scenarios to make sense. The MC isn't the true brother of Lucy and Sandra, but his presence in Rebecca's life is so that he would almost be a brother.
Just a thought because it kinda becomes weird to read landlady, landlord and tenant constantly lmao.